262 A HISTOEY OF EECENT CRUSTACEA 



distance from the apex, but generally reaching much 

 beyond it. Luminous globules are generally present on 

 various parts of the animal. The heart is furnished with 

 six pairs of lateral slits or venous openings. The develop- 

 ment is complex, the larva after hatching passing through 

 the Nauplius- and Zoea-stages. 



Eight genera are included in this family, three of which 

 are represented in the British Faima. 



Euphausia, Dana, 1852, which means 'a bright light,' 

 was so called in reference to the luminous character which 

 all the species of this genus share with most others in the 

 same family. This genus is distinguished from the rest 

 by having the last two pairs of legs quite rudimentary, 

 although the branchite are well developed. By the nume- 

 rous species it is almost universally distributed. It is 

 pelagic in habit, that is to say, its members occupy the 

 surface of the ocean when it suits them. They may or may 

 not descend to great depths, but often, and especially at 

 night time, they are to be found in great profusion at the 

 surface. Euphausia pellucida, Dana, a colourless species, 

 was met with ' in almost every tract of the ocean traversed 

 by the Challenger,' and has ako been taken in the Medi- 

 terranean and off the coast of Norway. Euphausia superba, 

 Dana, from the Antarctic Sea, has its whole body, except 

 the legs and branchise, tinged with a brilliant red. The 

 luminous globules in these animals were at one time sup- 

 posed to be accessory eyes, but Sars regards them as con- 

 stituting ' a very complicated and peculiarly developed 

 luminous or phosphorescent apparatus.' They are ' very 

 conspicuous in the living animal by reason of their beauti- 

 ful red pigment and glistening lustre.' The pigment coats 

 only the hinder half of the globule, which is filled up with 

 cellular matter enclosing a bunch of iridescent fibres, while 

 the front hemisphere is quite pellucid and contains a highly 

 refractive lenticular corpuscle. This last is supposed to 

 act ' as a condenser, producing a bright flash of light, the 

 direction of which admits of being changed at the will of 

 the animal, by simply rolling the organ by means of its 

 muscular apparatus.' 



